Keratoconus is a progressive eye disease that can cause distorted, blurry vision that often requires more complex contact lens solutions. This condition involves progressive thinning of the cornea (the front surface of the eye), causing the surface to protrude forward in a cone shape, giving the disease its name ("keras" meaning cornea, and "konos" meaning cone). With increased severity, the amount of protrusion and irregularity of the cornea increases.1
Keratoconus management is often reliant on early detection.2 At our Adelaide and Woodville practices, our optometrists have an interest in keratoconus, and one of our optometrists, Lachlan Hoy, has written the chapter on keratoconus in the globally distributed Contact Lenses textbook to be published in 2019. If you are interested in making an appointment, please contact us for more information.
Previously, the prevalence of keratoconus was estimated to be 0.05%3, however recent evidence cites the incidence to be as high as 0.26% in some populations.4 In Australia, keratoconus affects approximately 1 in 2000 people. Keratoconus generally presents during teenage years and progresses through to your forties, although the age at which it worsens varies from person to person.5 It is common for each eye to have a differing degree of severity.6
Family history is considered a risk factor, and according to one study the probability of being diagnosed with keratoconus if an immediate family member has the disease is 14%.7 Most studies indicate that no gender is more predisposed to the condition, but it is more prominent among patients with a personal history of allergy or eye rubbing. Often your optometrist will recommend certain anti-allergy eye drops to decrease symptoms of itchiness which cause keratoconics to rub their eyes and worsen their condition.8
Keratoconus is a multifactorial disease, hence the onset and progression can vary significantly between different people, and even between different eyes of the same person. Keratoconus is very unpredictable and can progress rapidly over a short period of time, before stabilising for months or years, then progressing again.9 For this reason, regular eye tests are recommended.
Our optometrists can assess the corneal (front surface of the eye) shape and thickness through microscopy. The below image shows a keratoconic cornea. Note the forward protrusion of the cornea, with notable thinning just below the centre. As well as changes in corneal shape and thickness, there are a number of other findings visible under microscopy. These include the presence of prominent corneal nerves, Fleischer’s iron ring and Vogt’s striae (corneal stress lines).10
Corneal topography is a non-invasive way to measure the contours and shape of the cornea. It is the ‘gold standard’ in diagnosing and assessing keratoconus.11 Topographers work by shining concentric rings of light on the cornea and assessing what is reflected back. If the cornea is even and regular, the rings are reflected back evenly.
The above images are the topographical results of a relatively normal cornea. Note the regular rings on the left image and the fairly concentric and uniformly coloured contour maps on the right image. Areas of yellow represent areas that are more curved on the eye. These images portray a regular cornea with no distortions or irregularities.
In contrast, these images are results from a topography taken of a significantly keratoconic eye. Note the distorted and compressed rings on the image on the left. The coloured contour maps of the same eye show a much darker red area over the centre of the eye, conveying the protrusion or ‘cone’ of the cornea. This has a significant impact on vision quality as the distorted surface is within the pupil zone (the black circle).
The OCT is an invaluable tool that allows practitioners to assess different layers of the eye as high-definition cross-sectional scans. This device was initially used to diagnose and manage macular degeneration and glaucoma at the back of the eye. More recent advancements in technology have enabled us to also utilise the precision of these scans for assessment of the front portion of the eye.
Due to the highly detailed images taken with an OCT, the different layers of the cornea are visible, as well as their configuration as the cornea protrudes forward (as shown above). As keratoconic eyes exhibit an overall thinning of the cornea at and around the cone, these layers are able to be measured and quantified to better monitor disease progression.
The OCT also helps us assess the relationship between contact lenses and the eye, to achieve the most ideal, comfortable and safe fitting contact lens.12 The above example of a custom scleral lens on the eye conveys adequate clearance over the cone and a nice smooth landing of the edge of the lens on the white part of the eye to ensure maximum comfort.
In rare situations someone with severe keratoconus can develop corneal hydrops, a condition where the posterior membrane of the cornea ruptures causing extreme corneal swelling, pain and ultimately scarring. Patients who have corneal hydrops often require a corneal graft due to the residual scarring.
If keratoconus is diagnosed early enough, a new surgical technique called collagen cross-linking (CXL) is often recommended. For this procedure, riboflavin (Vitamin B2) is soaked into a keratoconic cornea and activated by UV light. This promotes cross-linking of the collagen fibrils in the cornea, leading to a strengthening of the tissue. Collagen cross-linking will not cure someone of keratoconus and it may not improve the vision, but should stabilise the cornea, decreasing the chance of further thinning and damage.13 If your cornea has become too thin (~400um) then CXL is too unsafe to be carried out, so early referral is important.14
If the cornea becomes too thin or scars excessively over time, not even a perfect fitting contact lens may provide clear enough vision. In these instances a corneal graft may be required. The longer this can be delayed with contact lens wear and careful management the better – grafts have a risk of rejection, require long courses of steroid drops, and often require spectacles or contact lenses to be used after the surgery to see to the best level.
It is important for keratoconic patients to be assessed and fitted by an experienced optometrist with a strong background of keratoconus management. Our optometrists Lachlan Hoy, Karl Evans and Joanna Rohrlach have an interest in contact lens fitting and have treated many patients over the years with irregular corneas. Poorly fitting contact lenses have been shown to promote the progression of the disease in some individuals, due to an increase in inflammatory factors released into the tear fluid.15 Poorly fitting contact lenses can also cause permanent vision loss by scarring the cornea.16 Our optometrists use Innovative Contacts, a rigid lens production and distribution company that supplies optometrists all over Australia with an array of contact lens solutions for a multitude of refractive diseases, including keratoconus.
Pellucid Marginal Corneal Degeneration is an uncommon condition causing thinning of the lower part of the cornea. This non-inflammatory condition is often confused with keratoconus as it causes similar distortion of the cornea and requires complex contact lens designs, typically in the form of scleral lenses, to give the best quality of vision. Patients between the ages of 20-50 will often present with blurred vision due to the irregularity of their cornea. Often against-the-rule astigmatism is present and contributes to the blur seen. In PMCD, the stroma (collagen) of the cornea is abnormal and thin but the other parts of the cornea are unaffected and function normally. This degeneration can progress slowly over time, but will only very rarely progress to the point of perforating the cornea.
PMCD is best managed with large diameter scleral contact lenses that will vault over the affected area of cornea and still provide a regular front surface for vision. In severe cases a corneal graft may be needed to restore functional vision. Collagen cross-linking is a surgical procedure used in some progressive cases to prevent further worsening of the condition.